not sure about this but since Covid I don’t think posties need to get a signature before delivering a recorded delivery item - they just deliver it to the address shown.
I collect football programmes and often get them recorded delivery - I put a note near the letter-box asking the postie to sign on my behalf if a signature is needed. Strictly speaking I don’t think they should do this but anything is better then trailing to the main Sorting Office!
Having said that I don’tt hink your postie should have signed for your package without permission.